Main-group metal clusters approaches

Fused metal clusters are much more abundant than fused main-group clusters and Mingos developed an effective approach to their description (Section 3.3.3). His rule is that in fusing two clusters, the fragment formally eliminated must obey normal valence rules. Thus we have ... 

Atomistic simulations of the metal-oxide interface can be basically classified under two main groups depending on the representation of the substrate. The first approach is constituted by the cluster model, where a piece of material is made to represent the whole substrate. The second approach is the periodic approach where a selected part of the material is repeated in space thus taking advantage of the periodicity of the crystal (Fig. 2.1). 

Historically, the structural theory of borane and carborane clusters was developed first. This theory was later expanded to include clusters of the main group elements as well as those of the transition metals.This approach allowed the anticipation, in many cases, of the structure and the number of valence electrons of a given cluster as well as its mode of transformation during oxidation and reduction reactions. 

Main group elements form a wide variety of neutral, cationic, and anionic compounds having chain, ring, and cage structures (e.g. Zintl anions). [366] All of these may be useful starting materials to be combined with mono- and polynuclear transition metal moieties to generate molecules with novel and exciting structural features. This alternative type of synthetic approach has been used for the synthesis of all the other derivatives included in Table 3-11. For example, as shown in Scheme 3-12, the reaction of either Se4 or Te4 with such mononuclear metal carbonyls as [Fe(CO)s] and [W(CO)6] can yield cluster compounds... 

It became necessary to develop new approaches for predicting electron closed-shell structures, and ideas came from Williams, Wade, Mingos, and Rudolph, which now make up the polyhedral skeletal electron pair theory (PSEPT). The bonding in clusters can sometimes be described in terms of edge-localized, two-center two-electron bonds. Thus, through the formation of element-element bonds, the atoms of a polyhedron can acquire an effective inert gas configuration (8 valence electrons for a main group element and 18 for a transition metal atom). 

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